(a) Field of the Invention
The present invention refers to a new composition based on a natural, artificial and/or synthetic polymer, having self-extinguishing properties. In the description of the present invention, "synthetic polymer" means in particular a polyamide, a copolyamide, a polyester, or a copolyester; "artificial polymer" means in particular regenerated cellulose materials; and "natural polymer" means in particular cotton.
The present invention further refers to a process for rendering a composition based on said polymer or polymers, self-extinguishing, by adding a particular self-extinguishing additive, which will be better specified hereinafter, to the polymer itself, or, in the case of synthetic polymers, said additive may be added during the polymerization or before their transformation into formed materials. Further objects of the present invention will be indicated hereinafter.
(b) The prior art
It has been known for many years that the polymers of natural, artificial or synthetic origin constitute a danger because of their inflammability. This danger is particularly intensified in the case of textile materials, which contribute to a high percentage of accidents due to ignition of wearing apparel or textile products for furniture. The textile materials in regard to which the inflammability problem is particularly felt, are those derived from cellulosic fibres (rayon and/or cotton), synthetic fibres (such as polyamide, polyester) and also mixtures of cellulosic with synthetic fibres.
In general, in order to render a product self-extinguishing there exist mainly the following techniques:
(1) to use in the polymerization comonomers having self-extinguishing properties; and/or PA0 (2) to add substances having self-extinguishing properties to the polymers by means of extrusion operations in an extruder; and/or PA0 (3) to apply finishes containing self-extinguishing substances onto articles, e.g. fabrics, films, curtains, etc. PA0 (1) by addition during the polymerization to monomers which form polyamides and/or copolyamides, polyesters and/or copolyesters; PA0 (2) by addition in an extruder during the extrusion operation; the granules containing the additive may be used to obtain moulded bodies or may be used for melt spinning in order to obtain fibres and therefore textile manufacts which are self-extinguishing; PA0 (3) by application of finishes essentially comprising an aqueous suspension and containing a binder capable of binding product (A) onto the fabric under heating. PA0 (a) it is only slightly soluble in hot water (solubility less than 1 gr/lt), whereby the articles containing product (A) can maintain their self-extinguishing properties even after contact with water; PA0 (b) it has very high melting and/or degradation temperatures (above 300.degree. C.) and therefore it is possessed of a considerable thermal stability under the normal conditions of extrusion, moulding, polymerization, spinning of the materials for which it is intended; PA0 (c) it disperses homogeneously in the polyamides up to substantial concentrations, e.g. greater than 10% by weight with respect to the polyamide.
In order that one of methods (1) or (2) may be successful, it is necessary that the self-extinguishing agents employed should not produce or promote degradation reactions or other harmful reactions during the polymerization or whenever they are added. For instance, in the case of the polyamides, some types of products which impart self-extinguishing properties and which are used successfully for other classes of polymers, such as polyethyleneterephthalate, have proved to be unsuitable. Among these may be cited the halogenated compounds, in particular organic brominated or chlorinated compounds, which in the case of the polyamides cause a strong degradation of the polymer without significantly delaying the propagation of the flame.
Also certain phosphorated additives, which are notoriously self-extinguishing, especially in the presence of nitrogen containing substances, exert their self-extinguishing activity on the polyamides only when they are added in such high amounts as to affect negatively the peculiar characteristics of the polymer, such as spinnability, mechanical properties, color, etc.
Finally, certain substances containing nitrogen and sulphur, such as thiourea, ammonium sulphamate, thiocyanates, are not adapted for the polyamides when employed as comonomers or added by mixing them with the polymer in the molten state since they promote viscosity degradation and colour alteration of the polymer. For this reason such products or the polymers derived therefrom (urea, thiourea with formaldehyde and/or with melamine) are employed as self-extinguishing components only according to method (3), for polyamidic textile articles. Melamine, which confers to the polyamide a certain degree of flame retardant properties, has the disadvantage that it is not soluble in polycapronamide even at a concentration of 0.5%. Actually, the requirement of the homogeneity of the flame retardant agent in the polymer is fundamental, if the polymer is intended to be used as a fibre.
Therefore it is natural that when method (1) or (2) cannot be used to impart properties of resistance to the flame, it becomes necessary to resort to method (3), which consists in the application of self-extinguishing finishes. Such method further is the only one available for imparting self-extinguishing properties to certain products of cellulosic origin, such as cotton products.
It is also known that mixtures of fibres of cellulosic origin with thermoplastic fibres (polyester, polyamide fibers), are not self-extinguishing even if one fibre component has been treated with a self-extinguishing additive. Therefore for such mixtures it is advantageous to effect finishing treatments with additives that are effective to impart self-extinguishing properties both to the cellulose and to the thermoplastic fibre. In these cases however, the choice of the additive or additives is a difficult one because their activity, understood as the capability to impart self-extinguishing properties, is not the same for different materials.
A suitable solution for rendering a synthetic polymer (based on a polyamide or a polyester) self-extinguishing, when it is desired to employ self-extinguishing additives to be added to the molten polymer, consists in finding substances that will not cause undesirable thermodegradation of the polymer and will not negatively interfere with its colour and/or its physico-chemical and mechanical characteristics. Because of the many negative factors hereinbefore mentioned, the production of flame retarded or self-extinguishing polymers of the classes mentioned (polyamides and/or polyesters) by the addition of self-extinguishing compounds to the molten polymer and/or by copolymerization with self-extinguishing monomers, has remained a problem to the present time.